The present invention relates generally to a galvanic cell with a spiral-shaped electrode body, and more particularly, to an improved center pole conductor for such a cell, and its use in facilitating the winding procedure.
Spiral-wound galvanic cells are generally produced from windings of band-shaped positive and negative electrodes, with the imposition of a band-shaped separator, together with an appropriate current collector. A metal housing is provided to receive the spiral electrodes, one of which is electrically connected to the metal housing. The other electrode is electrically connected with a cover, which seals the opening of the housing and which serves as a terminal post for the associated electrode.
The conventional process for producing electrode windings of this general type makes use of a winding mandrel, usually a steel needle of about 5 to 7 mm in diameter, having a longitudinal slit which is used to engage the band electrodes. In most instances, this mandrel is permanently attached to the winding machine. Consequently, in operation, a free space is generally left in the middle of the electrode winding after its production, following withdrawal of the mandrel of the winding machine.
This free space, under certain circumstances (e.g., impact stressing of the cell), can lead to a displacement of the windings along the longitudinal axis of the cell, or even a mutual displacement of the electrodes. Attempts have been made to overcome this problem by using winding mandrels formed of plastic rods, which are designed to fill the free space in the electrode winding and provide a so-called "lost nucleus" for permanently positioning the windings (forming the basis for a compact arrangement of the electrodes).
However, in any event, it remains necessary to provide 10 the individual electrodes with separate current-conducting lugs, and to connect the lugs to their external cell poles (advantageously formed by the cell housing and cover). The production of such connections (which frequently must take the form of wire bridges) is rather difficult. What is more, a considerable transfer resistance can develop in the event of a faulty weld.
DE-C-2 438 296 discloses a somewhat more advantageous arrangement in which at least one electrode is connected to its respective terminal post by means of a terminal collector plate. However, such measures are only effective when the electrodes (e.g., a sintered foil strip) are not edged with an active paste, which could come into contact with the plate on the front side of the winding. DE-A-3 412 890, as well as DE-C-3 014 435, disclose wound electrode structures in which a winding core, originally used to produce the set of electrodes, also assumes the role of a terminal collector pole, as a current collector for a first one of the electrodes, while the housing serves as the terminal collector for the second electrode. However, the second electrode must then form the external side of the winding so that it can rest against the inner wall of the housing. DE-C-3 014 435 further discloses the placement of a coil spring onto the flange-like upper end of the cell's rod-like collector, which presses against the lower side of the metallic cell cover and accordingly establishes an electrical connection between the collector and its external pole. However, during assembly, this 10 spring requires special attention, particularly in its positioning on the head of the collector, since there is a danger that the coil spring will fly loose as the result of unintentional squeezing by the tool which is used to manipulate it. Such measures have therefore not proved to be entirely satisfactory.